help with itunes/buying apps!?

hi there guys, i just got my new touch and when i tryed to dwnload apps it wouldnt let me. i went and picked up a 20$ itunes gift card and reedemed it onthe itunes store, after that i could download the free apps only but not ones worth money. on the right hand side of itunes store it says my email, and that there is 20 $ but it still wont let me buy apps, what have i done wrong or are my billing settings messed up?

thanks

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also i just noticed i can buy songs and everything else but he apps. anyone no whats wrong?